When a voice recognition function is used, the voice recognition function is normally stopped so that a voice recognition system should not erroneously react to a sound therearound and instructions to start voice recognition are generally given when the voice recognition function is used. For example, a method of using a push to talk switch and enabling voice recognition only while the switch is pushed is known. As a method that does not use a switch, for example, Patent Literature 1 discloses a method of recognizing voice only for a fixed period of time after a user utters a specific keyword. In addition to the above method, methods of enabling voice recognition by utterance include, for example, a method of enabling voice recognition for a fixed period of time by uttering a predetermined keyword and a method of enabling voice recognition of voice following after a predetermined keyword is uttered. Hereafter, enabling to acquire voice to be recognized when the voice recognition function is used will be called “activating voice recognition”.